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(some of you will recognize me from a recent post, but now that we're starting over, let's start from the beginning.) I'm planning to install a new boiler, and I'm getting conflicting information on the "right" size. I believe the old boiler is too big. Here's what I know:

2 heat-loss models calculate loss to be about 60MBTUH. Rule-of-Thumb says about 96MBTUH.

Some contractors say, "size the boiler to match the installed radiation, other wise the bb at the end of the zone might be cold. Also, it's nice to know the capacity is there if you need it on the really cold days."

Dept of Energy says, "slightly undersizing a boiler ensures that it won't short cycle, and will always reach peak efficiency, it won't condense, it will last longer."

I live in SE PA. My gas bill during heating season averages $350/month. What size boiler do I need?

Simpleman meant something close

He means that you need to measure up and determine exactly WHAT your consequences would be.

Extra baseboard or radiation allows lower temperatures to be used; which spells higher efficiencies. Trouble is, if you go below a certain threshold, which is the best efficiency, you can destroy the chimney and boiler with flue gas condensation.

Don't do anything rash, just make a drawing up with loop lengths, diameters, and baseboard lengths on each loop. Design for the return temperature, and you'll be fine.

As you know, size the boiler to the heat loss. Don't pad it.

Extra baseboard, already installed, is a plus, rather than a negative. Use it wisely.

only 1 circ pushing into the boiler, TACO 007-F5, 1/25hp, 3250rpm, pushing into the boiler. . (I understand that this may be small.)

House stays warm on coldest days. One room in Zone2 is too hot. I believe it's simply over radiated compared to the other rooms in that zone. Zone4 is only one room, and it heats-up very quickly. It's a little uncomfortable, but only overshoots the t-stat by 1 degree.

Aquastat is set a 190. FYI, burners on the old boiler only run for 4-6 minutes.

First off, I'd lower the setting on the boiler's aquastat a bit, to about 175-180. That will increase the run time a little of the circulator.

If you are going to replace the boiler, I'd install one circ per zone. Yes, it's a little more, but the comfort level will increase. If the zone 2 loop is running by itself, that's probably when it overheats. I'd put a smaller circ on that zone and on the zone 4.

As long as the boiler stays above 140 degrees, you won't have a boiler condensing problem.

If you are planning on replacing the boiler, why don't you use a P/S piping system. Then put a mixing valve in the zones that are to hot. You can also put in an outdoor reset and get more eff. out of your system.

Its been my exp. that the old tale that BB needs to be supplied with 180* temps to convect heat is simply noy true. On design day temp. 180* may very well be needed and if designed properly should be met. However design day temps are not the norm, so supplying design day supply temps to convectors is simply wasting fuel and putting more stress on the system than is needed.Temp at 150* or even lower perhaps 10-15* lower would work. The problem occurs with lower water temps (120-130*) creating condensation in the flue pipe causing eventual HX failure due to deteroiration of flue pipe. Primary/secondary would solve that problem or go with a condensing boiler. IMHO.

I am going to use a crystal ball here, and tell you your home needs about 60K btu all told for heat. But please, do a room by room heat loss to confirm this. Further, my ball tells me you need about 100' of bb all told, maybe less. Again, do the calcs

If you are feeling ambitious, shorten the bb where needed-just for aesthetics and reduced dust collection alone! If not, could always put some aluminum foil/metal plates over the extra fins to keep the delta up..

The guys are right..size the boiler for the structure's heat loss. Then size the bb for each room's requirements.

Then..to soup up the system, you can do outdoor reset to tailor the bb's water temps to the temp outside.

Thank you for your replies. Lots of good information. Id like to nail-down some of the general info first, and then move to the details. I think I have questions on every response, so please bear with me.

First, I am replacing the boiler. Thats a given.
I did a room-by-room heat loss using software from a well-known bb mfr. (Thanks, Noel.) I have more than enough baseboard, so where appropriate Ill use Hydronicsmans idea of placing foil over the extra fins or close shutters where available. (The old cast iron stuff doesnt have a shutter.)

So if I plan for heat loss of 60MBTUH, do I select the boiler by its Output Rating or the IBR?

Beenthere: what outside air temp do you design for in Lancaster? (Its a little colder in Lancaster than it is in Philadelphia, but it should be close enough.)